In the process of global energy transition and the promotion of the "dual carbon" goal, the efficient operation of the power system is crucial. On January 15, 2025, the Yunnan Mile Wind Farm Flexible DC Project (referred to as the "Yunnan Mile Project"), led by the Three Gorges Corporation, was successfully connected to the grid. This project is the first large-scale use of 6.5kV integrated gate controllable thyristor (IGCT) devices, which has achieved a major breakthrough in flexible DC transmission technology, provided a new solution for the grid connection and consumption of new energy, and also demonstrated China's technological innovation capabilities in this field.
Ⅰ.Technical highlights of the Yunnan Mile project
The first large-scale application of 6.5kV IGCT devices
IGCT is a power semiconductor device with both low loss and high current capability, which is widely used in high-voltage and high-power scenarios. Yunnan Mile Engineering is the first in the world to use 288 domestic 6.5kV/4kA (2kA) IGCT-Plus devices, which has significant advantages compared with the existing international high-end flexible DC transmission technology:
1. Low loss: IGCT devices have 20%-30% lower conduction losses than traditional IGBTs, improving system efficiency.
2. High reliability: In high-altitude environments, the reduction of air density affects the insulation performance, while IGCT can operate stably and adapt to the complex climate and terrain conditions of Yunnan due to its excellent short-circuit tolerance and heat dissipation performance.
This device is developed by domestic leading enterprises, and comprehensively benchmarks international advanced technology. Its successful application proves the feasibility and competitiveness of domestic semiconductor technology in the field of high-end power.
Figure: Yunnan Mile Wind Farm Flexible DC Project was successfully connected to the grid
Innovative system architecture
The project uses a modular multilevel converter (MMC) system architecture with ± 15 kV, 60 MW back-to-back symmetrical unipolar wiring. The core benefits of the design include:
1. Improved system stability: The optimized design of the IGCT converter valve assembly significantly reduces the influence of harmonics in the grid and improves the quality of power supply.
2. Reduced operating costs: The overall loss of the converter valve is reduced by more than 30%, and the equipment footprint is reduced by nearly 20%, achieving a balance between economy and technical performance.
3. Modular design: It supports flexible expansion to meet the needs of larger-scale new energy grid connection in the future.
Through this innovative design, Yunnan Mile Engineering has set a new benchmark for the application of flexible DC technology, and provided a replicable example for subsequent technology upgrades.
Ⅱ.The role of the project in promoting the "double carbon" goal
The capacity of new energy consumption has been significantly improved
The flexible DC transmission system can quickly respond to the needs of the power grid and independently control the active and reactive power, which is especially suitable for the grid connection of fluctuating new energy sources such as wind power and photovoltaics. In the Yunnan Mile Project, the flexible DC technology greatly reduces the curtailment of wind and electricity.
For example, data shows that the average annual curtailment rate in Yunnan is more than 10%, and this proportion is expected to drop to less than 3% after the Mile project is put into operation. This not only optimizes the efficiency of regional energy utilization, but also provides valuable experience for the national new energy grid-connected technology.
Significant energy saving and emission reduction benefits
Compared with traditional AC transmission, flexible DC transmission technology has higher transmission efficiency. The Yunnan Mile project can reduce the consumption of standard coal by about 30,000 tons per year, and the corresponding carbon dioxide emission reduction is about 80,000 tons. The specific performance is as follows:
1. Reduced energy loss: The efficient operation of the IGCT converter valve reduces the loss of electrical energy in the transmission process.
2. Reduced equipment investment: IGCT devices with higher voltage levels have miniaturized converter stations, reducing land and construction costs.
Through these advantages, the project provides strong support for China's energy conservation and emission reduction strategy, and also reflects the great potential of flexible DC technology in ecological environmental protection.
Ⅲ.It is of far-reaching significance to the development of flexible DC technology in China
A breakthrough in technological innovation
From the research and development of localized 6.5kV IGCT devices to the overall integration of flexible DC systems, Yunnan Mile Engineering has overcome many technical problems:
1. Breakthrough in IGCT device technology: It realizes the design of higher power density and lower loss, and overcomes the technical barriers of high-voltage packaging and drive control.
2. System integration optimization: For high-altitude working conditions, the converter valve, heat dissipation and control system of the flexible DC system are customized to ensure the reliability of the equipment.
These achievements not only consolidate China's global competitiveness in the field of flexible DC technology, but also lay a solid foundation for subsequent technology promotion and engineering application.
Promote the coordinated development of the industrial chain
The successful application of flexible DC technology will further promote the coordinated development of the upstream and downstream industrial chains. Taking the Mile Project as an example, the core enterprises in related fields have achieved technological breakthroughs in power semiconductors, packaging equipment, electronic components, etc., which has led to the overall industrial upgrading.
1. Semiconductor industry: The successful application of domestic IGCT devices marks that China's power semiconductor technology has entered the world's leading ranks.
2. Equipment manufacturing industry: The integration of flexible DC systems has promoted the process of intelligent and localization of power equipment.
At the same time, the project has also injected new momentum into the regional economic development and created a large number of high-tech employment opportunities.
Ⅳ.Future outlook
Technological upgrading and intelligent development
In the future, flexible DC technology will evolve in the direction of higher voltage, larger capacity, and intelligence. For example, research on ± 800 kV flexible DC transmission technology has begun to bear fruit, which will significantly improve the efficiency and economy of long-distance power transmission. At the same time, the combination of artificial intelligence and Internet of Things technology will realize the precise control and intelligent operation and maintenance of the flexible DC system, and further improve the reliability and flexibility of the system.
The application scenarios are constantly expanding
The application potential of flexible DC technology extends far beyond the field of new energy. In the future, this technology will play a more important role in scenarios such as urban power grid upgrades, offshore wind power development, and power transmission in special climate environments.
For example:
1. Urban power grids: Flexible DC transmission can be used to alleviate the load pressure on the power grid in urban centers.
2. Offshore wind: Efficient transmission technologies can help solve bottlenecks in power transmission in offshore wind farms.
These new applications will further strengthen China's global leadership in flexible DC technology.
Ⅴ.Conclusion
The official grid connection of the Yunnan Mile project is an important milestone in the development of flexible DC technology in China, demonstrating China's strong innovation ability in the field of power semiconductors and power systems. With the continuous advancement of technology and the expansion of application scope, flexible DC technology will play a more important role in promoting the "dual carbon" goal, accelerating the energy transition, and optimizing the power system.
